The present invention relates generally to the field of work vehicles. It relates more particularly to a system for cooling of hydraulic fluids of a work vehicle.
Work vehicles used in construction and agriculture often include two hydraulic circuits provided with different fluids. In many instances, the first hydraulic circuit is a transmission (e.g., an automatic transmission with a torque converter or a hydrostatic transmission) and the second hydraulic circuit is a tool hydraulic circuit; e.g., a system fluidly driving the buckets, linkages, boom, dipperstick, etc. of a tractor mounted backhoe/loader. The transmission has fluid characteristic needs differing from those of the tool hydraulic circuit, and there are therefore two separate fluid circuits, provided with differing fluids which should not be mixed, on the work vehicle.
In such work vehicles, each hydraulic circuit will usually have its own fluid cooler. Cooling system efficiencies must often be compromised due to lack of space on the work vehicle to place two separate coolers, each of capacity adequate for its hydraulic circuit. The coolers provided are therefore often of capacities which are marginal at best, and sometimes inadequate with heavy work loads in hot weather.
Again referring to the example of the backhoe-loader, the largest heat load generated in the tool hydraulic circuit occurs when the backhoe is worked very hard in high ambient temperatures. During this backhoe operation, the transmission heat load is very small. Conversely, the largest transmission heat loads occur during high-speed roading or during very heavy loader work involving dozing or other high push efforts. During this roading or loader work the tool hydraulic circuit is generally developing very little heat.
Another problem sometimes arises in frigid winter weather in some locations, related to cold, stiff, viscous fluid. Heat rejected at a fluid cooler could well be used to maintain the temperature of the fluid in the other circuit in order to improve wear life of that circuit""s components and to improve overall efficiency of the work vehicle.
It would be advantageous to provide for a work vehicle having two, or more, hydraulic circuits with differing fluids to have a capability of transferring heat from whichever of the fluids is hotter to the other fluid. It would also be advantageous to provide for a work vehicle to have a cooling system fully adequate for all conditions of operation without increasing size of a fluid cooler. It would further be advantageous to provide for a work vehicle to maintain an unloaded hydraulic circuit at a working temperature during frigid weather.
One embodiment of the invention relates to a work vehicle including a vehicle structure, a power source supported by the vehicle structure, a plurality of wheels rotatably secured to the structure for supporting the structure upon a surface and rotatably coupled to the power source for moving the vehicle across the surface. The work vehicle also includes a first hydraulic circuit including a first fluid, the first fluid being heated by a first mechanical system of the work vehicle; and a second hydraulic circuit including a second fluid, the second fluid being heated by a second mechanical system of the work vehicle. The first and second hydraulic circuits are configured to maintain the second fluid separate from the first fluid. The work vehicle further includes at least one fluid cooler for cooling one of the first and second fluids; as well as an apparatus for transferring heat from the first fluid to the second fluid when the first fluid is hotter than the second fluid and for transferring heat from the second fluid to the first fluid when the second fluid is hotter than the first fluid.
Another embodiment of the invention relates to a fluid cooling apparatus for a work vehicle. The work vehicle includes a power source and a transmission for moving the vehicle across a surface. The transmission is provided with a transmission fluid. The work vehicle further includes a tool hydraulic circuit, the tool hydraulic circuit including a hydraulic fluid. One of the transmission fluid and the hydraulic fluid is operatively hotter than the other of the transmission fluid and the hydraulic fluid. The cooling apparatus includes at least one fluid cooler for cooling at least one of the transmission and the hydraulic fluids, and an apparatus for transferring heat from the hotter of the transmission and hydraulic fluids to the other of the transmission and hydraulic fluids.
Another embodiment of the invention relates to a method of cooling a plurality of fluids of a work vehicle provided with at least a first hydraulic circuit including a first fluid and a second hydraulic circuit including a second fluid. The first and second hydraulic circuits are configured to maintain the second fluid separate from the first fluid. One of the first and second fluids is hotter than the other of the first and second fluids. At least one of the first and the second hydraulic circuits further includes a fluid cooler for cooling the first or the second fluid respectively and a pump for circulating the first or the second fluid respectively through the fluid cooler. The vehicle is further provided with a heat transfer apparatus for transferring heat from the hotter of the first and the second fluids to the other of the first and the second fluids. The method includes the steps of using the pump to circulate the first or the second fluid through the fluid cooler, and using the pump to circulate the first or the second fluid through the heat transfer apparatus.